Fiber optic cable system including main and drop cables and associated fabrication method

ABSTRACT

A fiber optic cable system, such as a preterminated fiber cable, includes a main cable and one or more drop cables connected to the main cable at spaced apart locations along the main cable. The drop cable is spliced to the main cable using a splice closure including a fiber guide that secures spliced together end portions of the respective fibers in a longitudinally extending direction and devoid of any slack coils of optical fibers. Accordingly, the overall diameter of the splice closure is relatively small thereby permitting the cable system to be stored on a reel and to be readily placed within small diameter conduits. The splice closure includes a heat recoverable housing surrounding the fiber guide. Cable sheath end portions are sealed by melting C-shaped bodies of heat flowable material positioned adjacent cable sheath end portions.

This application is a division of application No. 08/048,610 filed Apr.16, 1993, now U.S. Pat. No. 5,460,665, the disclosure of which isincorporated by reference.

FIELD OF THE INVENTION

The invention relates to the field of fiber optic communicationssystems, and more particularly, to a fiber optic cable system andassociated methods.

BACKGROUND OF THE INVENTION

Fiber optic cables are widely used for telecommunications applicationswhere high information capacity, noise immunity and other advantages ofoptical fibers may be exploited. Fiber cable architectures are emergingfor connecting homes and/or business establishments, via optical fibers,to a central location, for example. One such architecture includes atrunk or main cable routed through a housing subdivision, for example,while small fiber count "drop cables" are spliced to the main cable atpredetermined spaced apart locations.

A typical main cable may be installed underground and have multiple dropcables connected thereto, each of a hundred feet or more. Each of thedrop cables, in turn, is routed to an optical network unit (ONU) servingseveral homes. Accordingly, information may be transmitted optically tothe ONU, and into the home via conventional copper cable technology.Thus, the drop cables may serve groups of users, although otherarchitectures may also employ a main cable and one or more drop cablesconnected thereto.

Unfortunately, the fibers within the main cable must typically beaccessed at the various drop points and spliced to respective dropcables after the main cable has already been installed. Accessing themain cable for splicing requires careful preparation of the main cableincluding removing a portion of the cable sheath, and identifying andseparating out predetermined fibers from within the cable withoutdisturbing adjacent fibers. The separated fibers may then be spliced andsecured within a conventional protective splice closure. Moreover, thesecable access and splicing steps must typically be accomplished in thefield by a technician who is likely to experience difficulties imposedby weather or the particular location of each of the drop points.Accordingly, field splicing of drop cables to a main cable is timeconsuming, expensive, and may produce low quality optical splices.

In an effort to overcome the disadvantages of field splicing drop cablesat each of a series of drop points, so-called preterminated fiber opticcables have been proposed. A preterminated fiber optic cable includes arelatively high fiber count main cable to which respective low fibercount drop cables are spliced at predetermined drop points. Thelocations of the drop points are determined based upon field surveymeasurements.

The splicing of the drop cables to the main cable of a preterminatedcable is performed at the factory during manufacturing of the cable. Thepreterminated cable, including the main cable, drop cables, andassociated splice closures, are desirably wound onto a cable reel anddelivered to the installation site. Accordingly, conditions for makinghigh quality splices may be maximized in the factory, thereby increasingsplice quality and also reducing the expense and difficulty associatedwith field splicing.

Exemplary of a preterminated cable is U.S. Pat. No. 5,121,458 to Nilssonet al. entitled Preterminated Fiber Optic Cable. The patent discloses asplice closure for splicing each of the drop cables to the main cable.The splice closure is generally cylindrical being no greater than 4inches in diameter and 7 inches in length to facilitate winding of thepreterminated cable, including the associated splice closures, onto acable reel for shipping and installation. In particular, the patentdiscloses that the diameter of the splice closure is slightly less than4 inches in diameter so that the preterminated cable may be installedthrough a 4 inch conduit.

The splice closure as disclosed in U.S. Pat. No. 5,121,458 uses aconventional technique for storing slack fibers within the spliceclosure, that is, the slack is stored in slack coils or loops. The slackcoils must be made without violating the minimum bend radius of thefibers. Accordingly, the splice closure still must have a relativelylarge outer diameter which hampers winding of the splice closures ontothe cable reel, and which may also greatly complicate installation ofthe cable within a section of buried conduit. For example, conduits lessthan 4 inches are commonly used for placing a conventional fiber opticor copper cable to facilitate installation under obstructions, such as adriveway. In addition, small diameter conduits are also desirably usedto reduce excavation time and expense when installing the conduit.

U.S. Pat. No. 5,125,060 to Edmundson entitled Fiber Optic Cable HavingSpliceless Fiber Branch and Method of Making Same discloses anotherapproach in an attempt to overcome the difficulties in reducing the sizeof the connection or branching point of the drop cables from the maincable. The patent discloses spliceless stub cables extending from themain cable. More particularly, an opening is made in the jacket of themain cable at a disconnect point downstream from the intended branchingpoint. The fibers to be branched for the stub cable are severed andpulled back through the branching point. The branched fibers are routedthrough a stub cable sheath and the disconnect point of the cable issealed. The penetration into the main cable sheath, as well as its jointwith the stub cable sheath are sealed at the branching point by aplastic housing. Thus, no splices are required and no slack opticalfibers need be stored within the protective housing at the branchingpoint.

Unfortunately, the approach disclosed in U.S. Pat. No. 5,125,060 suffersfrom a significant drawback in that the stub cable extending from themain cable is limited to only about 12 feet in length. Accordingly, fora typical fiber optic cable system route, a conventional splice is stillneeded to add an additional length of cable to the stub cable, and thesplice must still be made in the field by a technician. Another drawbackof the approach disclosed in U.S. Pat. No. 5,125,060 is thatconsiderable care must be taken when pulling the 12 foot lengths offibers back through the branching point during preparation of the stubcables. A corresponding difficulty is encountered when stuffing the 12foot lengths of fibers into the stub cable sheath. The main cable sheathis also penetrated 12 feet downstream from the branching point at thedisconnect point, and this cable penetration must also be sealed toprotect the cable from water entry.

Because the fiber optic cable systems described above includepenetrations of the cable sheath, it is important to seal suchpenetrations to prevent water from entering the cable and damaging theoptical fibers particularly at a splice location. One approach tosealing a splice point is disclosed in U.S. Pat. No. 5,125,060 whichdescribes a heat recoverable housing surrounding the branch point fromwhich the short stub cables extend. Similarly, U.S. Pat. No. 5,121,458discloses a heat recoverable housing surrounding the splice closurewhich, in turn, stores the coils of slack cable in a conventionalfashion.

U.S. Pat. No. 5,185,844 to Bensel, III et al. entitled Closure forOptical Fiber Connective Arrangements and Method for Making Samediscloses a splice closure for joining together only two small fibercount cables in an in-line configuration with very little slack in theoptical fibers. Thus, the closure is not suitable for splicing a dropcable to a main cable as in a preterminated fiber optic cable.

SUMMARY OF THE INVENTION

In view of the foregoing background, it is therefore an object of thepresent invention to provide a fiber optic cable system and associatedfabrication method including a relatively compact splice closure forjoining one or more drop cables to a main cable so that the entire cablesystem may be readily wound upon a cable reel and readily installedwithin a typical conduit system.

It is another object of the present invention to provide a fiber opticcable system which is effectively sealed where the cables enter theinterior of the splice closure to protect the splices from water damage,such as caused by water migration from the cable end.

These and other objects, advantages, and features of the presentinvention are provided by a fiber optic cable system including a maincable and a drop cable joined together at a splice closure, wherein atleast one spliced together fiber portion is guided in a generallylongitudinal path adjacent the main cable, and wherein the splicedtogether fiber portion is devoid of a slack coil of optical fibers.Accordingly, the outer diameter of the splice closure may be made verysmall so as to be readily accommodated within typical conduits and to bereadily wound onto a conventional cable reel. For example, the spliceclosure according to the present invention may be fabricated having anouter diameter of less than about 1.8 inches.

The fiber optic cable system as described herein includes apreterminated cable system as may preferably be manufactured in afactory setting. As would be readily understood by those skilled in theart, the fiber optic cable system according to the present invention mayalso include a system wherein the drop cable and associated splice aremade to the main cable in the field.

More particularly, the fiber optic main cable includes a longitudinallyextending buffer tube having an opening at a first location, and atleast one optical fiber having an end portion extending through theopening. As would be readily understood by those skilled in the art, themain cable may be of the type having a plurality of stranded buffertubes or a single centrally located buffer tube. The main cable istypically a high fiber count cable of greater than about 48 fibers.

The fiber optic drop cable has an end secured to the main cable at asecond location downstream from the first location. The drop cableincludes at least one fiber and is typically a low fiber count cablehaving two or four fibers. An end portion of at least one optical fiberextends outwardly from the end of the drop cable. The at least one fiberend portion of the drop cable is spliced together with the at least oneend portion of the fiber of the main cable by a conventional splicingtechnique, such as fusion splicing, and thereby define at least onespliced together fiber portion. Accordingly, the splice closuresurrounds and protects the at least one spliced together fiber portion.Since it is typical that the drop cable and main cable would include twoor more fibers spliced together, the plural term "fibers" is sometimesused herein, it being understood that a splice between even singlefibers is contemplated by the invention.

The fiber guide means preferably includes an elongate tube having alongitudinally extending slot therein which receives the splicedtogether fiber portions. In addition, the drop cable preferably includesa central buffer tube having an end portion of its buffer tubepositioned within an adjacent end portion of the elongate tube of thefiber guide means. The fiber guide means also preferably includes a pairof longitudinally extending arcuately shaped walls connected to theelongate tube and gripping adjacent portions of the main cable. Theelongate tube and arcuately shaped walls may be integrally moldedplastic, for example.

A foam cushion layer is preferably provided underlying the arcuatelyshaped walls of fiber guide means to serve as a cushioning layer. Aplurality of longitudinally spaced apart fasteners, such as tie wraps,may surround the main cable and the pair of arcuately shaped walls tosecure the fiber guide means to the main cable.

As would be readily be understood by those skilled in the art, the fiberoptic main cable may preferably include a metallic shield surroundingthe one or more buffer tubes. Accordingly, to permit access to apredetermined buffer tube for removing the end portions of the opticalfibers, a longitudinally extending portion of the metallic shield ispreferably removed from the main cable. The discontinuous metallicshield defines first and second cable shield end portions adjacentrespective ones of the first and second locations along the main cable.Accordingly, the splice closure of the present invention preferablyincludes electrical connection means extending between the first andsecond metallic shield end portions and connected thereto formaintaining electrical continuity of the metallic shield.

The electrical connection means preferably includes a length of wire,and first and second bonding clamps securing opposing ends of the wireto respective first and second metallic shield end portions. Theelectrical connection means may thus be provided without adverselyimpacting the overall outer diameter of the splice closure. Yet anotherfeature of the invention is that the second bonding clamp preferablyincludes a strap encompassing the end of the drop cable for securing thedrop cable to the main cable. In an embodiment of the inventionincluding a single buffer tube, such as in an LXE® cable by AT&T,longitudinal strength members may be cut and tucked under an adjacentportion of the shield. Alternately, a bonding clamp may be used of thetype described in copending application entitled FIBER OPTIC BONDINGASSEMBLY AND ASSOCIATED METHOD, assigned to the assignee of the presentinvention, the entire of disclosure of which is incorporated herein byreference.

A longitudinally extending portion of the cable sheath is alsopreferably removed from the main cable and defines first and secondcable sheath end portions adjacent respective ones of the first andsecond locations along the main cable. Moreover, the splice closure alsopreferably includes a heat recoverable housing surrounding the maincable and extending between the first and second cable sheath endportions to prevent water entry into the closure. The splice closurealso preferably includes a heat shield layer underlying the heatrecoverable housing for providing mechanical protection and forprotecting the fiber guide means and other underlying components whenheating the housing to cause the housing to shrink to its finaldimensions.

Another aspect of the present invention is that the splice closurepreferably includes sealing means contained within the heat recoverablehousing adjacent respective first and second cable sheath end portions.The sealing means serves to prevent water migration into the spliceclosure from the cable sheath end portions. The sealing means alsopreferably includes first and second masses of heat flowable materialsurrounding the cable and filling any voids adjacent respective firstand second cable sheath end portions.

To prevent flow of heat flowable material into the fiber guide whenmelting the heat flowable material, the sealing means also preferablyincludes respective blocking dams adjacent opposing ends of the fiberguide means. The blocking dams preferably include a layer ofcompressible material, such as a wound strip of foam material,surrounding the main cable. The blocking dams permit less heat flowablematerial to be used to protect the splices and help to reduce the needfor a larger diameter splice closure.

To further facilitate sealing of the cable sheath end portions for astranded buffer tube cable, concentric spacers surround respectivepredetermined ones of the buffer tubes for maintaining the buffer tubesin spaced apart relation. The spacers are preferably positioned onalternating tubes in a staggered relation. The thus spaced apartrelation of the buffer tubes facilitates flow of the heat flowablematerial into voids between the buffer tubes.

According to another aspect of the invention, the sealing means and aheat recoverable tube define a sealing arrangement that may be used inother applications for sealing an end of a fiber optic cable, such asfor a cable entry into a conventional splice closure. The protectivesealing arrangement preferably includes a blocking dam surrounding oneor more buffer tubes longitudinally spaced apart from the cable sheathend portion, a heat recoverable tube surrounding the fiber optic cablebetween the cable sheath end portion and the blocking dam, and at leastone C-shaped body of heat flowable material which is melted and flows tofill voids underlying the heat recoverable tube.

A plurality of concentric spacers, as discussed above, preferablysurround predetermined ones of the buffer tubes for a stranded cabledesign. The spacers position the buffer tubes in spaced apart relationto facilitate flow of said heat flowable material into voids between thespaced apart buffer tubes. The heat recoverable tube may also be atransparent material to permit viewing into the interior of the tube toassure proper flow of the heat flowable material upon heating. A bondingclamp may also be secured to a metallic shield portion of the cable forbonding or grounding of the cable shield.

Another aspect of the present invention is a combined strain relief andguide means preferably positioned on each end of the housing of a spliceclosure to provide both strain relief and to assist in guiding theenclosure through a conduit, for example. While the strain relief maypreferably be used in combination with the splice closure for the mainand drop fiber optic cables as described above, those of skill in theart will readily understand that the strain relief may be used in othersplicing arrangements as well, such as in conventional copper cablesplices.

More particularly, the cable has a first degree of flexibility, while aheat recoverable housing surrounding the cable splice will have a seconddegree of flexibility higher than the first degree of flexibility of thecable. The housing also includes an end opening through which a portionof the cable emerges. The strain relief is secured to the emergingportion of the cable immediately downstream from the end opening of thehousing to provide strain relief to the emerging cable portion. Thestrain relief means includes an elongate body and means for securing theelongate body to the emerging cable portion. The elongate bodypreferably has a predetermined degree of flexibility, for producing incombination with the emerging cable portion, a third degree offlexibility between the first and second degrees of flexibility tothereby provide strain relief to the emerging cable portion.

The housing is preferably provided by a sheet of heat recoverablematerial having a pair of abutting longitudinally extending edgeportions, and a clamp member for securing the edge portions togetherthereby defining an enlarged circumferential portion for the housing.Accordingly, the elongate body preferably further includes alongitudinally extending tapered portion aligned with the enlargedcircumferential portion for facilitating passage of said splice closurethrough a conduit. In one embodiment of the invention, the elongate bodypreferably includes a second or tapered distal end portion for furtherfacilitating passage of the splice closure through a conduit. Theelongate body also preferably includes a proximal end portion extendinglongitudinally into the end opening of the heat recoverable housing andbetween the cable and the housing, thus, providing even greater strainrelief capability.

In another embodiment of the invention, the clamp member has an endportion extending longitudinally outwardly a predetermined distancebeyond adjacent edge portions of the sheet of heat recoverable material.Accordingly, a portion of the elongate body adjacent the tapered portionhas a recess therein receiving therein the end portion of the clampmember. A tape wrapping or another fastener may be used to secure theelongate body to the cable.

A method for making the fiber optic cable system as described aboveincludes the steps of withdrawing end portions of the optical fibers ofthe main cable outwardly from a buffer tube at a first location alongthe main cable. The end portions of optical fibers of the drop cable arespliced with respective end portions of the predetermined optical fibersof the main cable to form spliced together fiber portions. The splicedtogether fiber portions are secured adjacent the main cable in agenerally longitudinally extending direction so that the splicedtogether fiber portions are devoid of a slack coil of optical fiber.

The method also preferably further includes the step of securing the endof the fiber optic drop cable to the main cable at a second locationdownstream from the first location. Accordingly, the step of securingthe spliced together fiber portions preferably includes positioning afiber guide extending in a generally longitudinal direction adjacent themain cable between the first and second locations thereof.

The fiber guide preferably is provided by an elongate tube having alongitudinally extending slot therein, and the step of securing thespliced together fiber portions includes positioning the splicedtogether fiber portions through the longitudinal slot of the elongatetube. The splicing step preferably includes preparing the respectivefiber end portions so that the spliced together fiber portions have asubstantially corresponding length to the elongate tube.

The drop cable also preferably includes a longitudinally extendingbuffer tube. Accordingly, the step of securing the drop cable to themain cable preferably includes inserting a portion of the drop cablebuffer tube into an adjacent end of the elongate tube.

As discussed above, the cable is preferably of the type including ametallic shield and outer sheath that are removed substantially betweenthe first and second locations along the main cable. Accordingly, theelectrical continuity of the metallic shield is preferably maintained byconnecting the shield end portions. The method also preferably includesthe step of positioning a heat recoverable housing surrounding the maincable between the first and second cable sheath end portions.

As would be readily understood by those skilled in the art, the step ofwithdrawing end portions of the optical fibers of the main cablepreferably includes severing same adjacent the second location along themain cable downstream from the first location along the main cable. Fora typical splice, the separation between the first and second locationsmay be about a foot which provides sufficient fiber length to performseveral splices if a remake is necessary.

Another method aspect according to the invention is for making theprotective sealing arrangement for a fiber optic cable as described ingreater detail above. The method may be used for sealing a cable end asin the splice closure for the main and drop cables, or the method may beused for a cable end entering a conventional splice closure. The methodpreferably includes the steps of positioning a blocking dam surroundingthe one or more buffer tubes longitudinally spaced apart from a cablesheath end portion; positioning at least one body of heat flowablematerial surrounding the buffer tubes between the blocking dam and thecable sheath end portion; positioning a heat recoverable housingsurrounding the fiber optic cable between the cable sheath end portionand the blocking dam; and heating the heat recoverable housing to shrinkthe housing and melting the heat flowable material to cause the heatflowable material to fill voids underlying the housing.

The body of heat flowable material is preferably C-shaped so that thestep of positioning the body surrounding the fiber optic cablepreferably includes inserting the fiber optic cable into an opening ofthe C-shaped body. The heat recoverable housing also serves to compressthe C-shaped body upon melting to thereby force the material to flow tofill underlying voids.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective schematic view of a fiber optic cable systemaccording to the present invention being payed out from a cable reel andillustrating a drop cable connected to a main cable at a splice closure.

FIG. 2 is an enlarged exploded perspective view of the splice closureaccording to the present invention.

FIG. 3 is a greatly enlarged exploded perspective view of a cable sheathend portion and metallic shield end portion as shown in FIG. 1 andillustrates positioning of a portion of a metallic shield bonding clampmember thereto.

FIG. 4 is a greatly enlarged exploded perspective view of a cable sheathend portion and metallic shield end portion as shown in FIG. 3 andillustrates installation of other metallic shield bonding clampportions.

FIG. 5 is a greatly enlarged cross-sectional view taken along lines 5--5of FIG. 2.

FIG. 6 is a greatly enlarged cross-sectional view taken along lines 6--6of FIG. 2.

FIG. 7 is a greatly enlarged perspective fragmentary view of a portionof the fiber guide means and underlying main cable portion according tothe invention with the heat shield and outer heat recoverable housingremoved for clarity.

FIG. 8 is a greatly enlarged perspective view of spaced apart first andsecond locations along the main cable illustrating separation of opticalfibers from a buffer tube according to the invention.

FIG. 9 is a greatly enlarged exploded perspective view of a portion ofthe fiber guide means adjacent the first location along the main cableaccording to the invention and illustrating routing of the separatedoptical fibers in the fiber guide means.

FIG. 10 is a greatly enlarged perspective view of a portion of the fiberguide means illustrating portions of the spliced together fiber portionsaccording to the invention.

FIG. 11 is a greatly enlarged perspective view of an end portion of thesplice guide at a second location along the main cable and illustratingconnection to a buffer tube of the drop cable according to theinvention.

FIGS. 12-14 are a greatly enlarged cross-sectional views of a portion ofthe main cable illustrating sealing thereof and the sealing arrangementaccording to the present invention.

FIG. 15 is a flowchart block diagram of a method of fabricating thefiber optic cable system of the present invention.

FIG. 16 is an enlarged cross-sectional view of an alternate embodimentof the fiber guide means according to the invention.

FIG. 17 is a perspective view of a portion of a single buffer tube cableincluding longitudinal strength members and illustrating how thestrength members may be captured according to one aspect of theinvention.

FIGS. 18-20 are perspective views of an end portion of the housingaccording to the invention illustrating a first embodiment of a strainrelief or cable guide means being secured to an end of the spliceclosure housing.

FIGS. 21 and 22 are perspective views of an end portion of the housingaccording to the invention illustrating a second embodiment of a strainrelief or cable guide means secured to an end of the splice closurehousing.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will now be described more fully hereinafter withreference to the accompanying drawings, in which a preferred embodimentsof the invention are shown. This invention may, however, be embodied inmany different forms and should not be construed as limited to theembodiments set forth herein. Rather, applicants provides theseembodiments so that this disclosure will be thorough and complete, andwill fully convey the scope of the invention to those skilled in theart. Like numbers refer to like elements throughout.

Referring first to FIG. 1, the fiber optic cable system 20 according tothe present invention includes a fiber optic main cable 21 and a fiberoptic drop cable 22 connected thereto at a splice closure 24. As wouldreadily be understood by those skilled in the art, the main cable 21preferably has a relatively high fiber count, such as 48 fibers, whilethe drop cable 22 is typically a low fiber count cable, such as 2 or 4fibers. As illustrated, the cable system 20 may be installed so that oneor more drop cables extend to desired locations, such as a residence oran ONU, along the route of the main cable 21.

As also illustrated in FIG. 1, the fiber optic cable system 20 may bereadily wound onto a conventional cable reel 25 during manufacturing,and delivered and installed in the field from the cable reel, because ofthe relatively compact outer diameter of the splice closure 24, that is,less than about 1.8 inches. The fiber splice closure 24 is also somewhatflexible and permits the splice closure to bend slightly to conform tothe curvature of the cable reel 25.

Although the cable system 20 according to the present may advantageouslybe assembled in the factory as a preterminated optical fiber cable,those of skill in the art will readily appreciate that the spliceclosure 24 and techniques described herein may also be readily used forconnecting drop cables along a main cable already installed in thefield.

Referring now to FIGS. 2 through 5, several components of the spliceclosure 24 are described. The main cable 21 may be either of thestranded loose buffer tube type, as shown, or the single central buffertube type, as would be readily understood by those skilled in the art.The stranded loose buffer tube cable includes a plurality of buffertubes 26 stranded around a plastic coated central supporting member 27.A longitudinally extending portion of the cable sheath 31 and theunderlying metallic shield 32 are removed from the main cable 21 toexpose the underlying buffer tubes 26. As shown best in FIG. 3, the maincable 21 may also be of the type having an aramid yarn covering 29surrounding the buffer tubes 26 for strength, and a polyethylenecovering 30 positioned between the aramid yarn covering 29 and themetallic shield 32. Fiber guide means 34, as described in greater detailbelow, is secured adjacent the buffer tubes 26 exposed along the openedportion of the main cable 21. The fiber guide means 34 carries thespliced together fiber portions of the main and drop cables.

A heat shield 37, and heat recoverable housing 38 along with itsassociated clamp member 39 are positioned to surround the main cable 21to protect the exposed open sheath portion thereof and the fiber guidemeans 34. As would be readily understood by those having skill in theart, the heat shield 37, housing 38 and clamp 39 may preferably be ofthe conventional type as used in copper cable repair and splicing. Forexample, the heat recoverable material may be a woven sleeve productsold by the assignee of the present invention under the designationXAGA® 550, or an extruded sleeve product sold under the designationXAGA® 500. Strain relief or guide means 40 may be positioned on theopposing ends of the splice closure 24 to facilitate pulling the spliceclosure through a conduit, as described more fully below.

The heat recoverable housing 38 in the illustrated embodiment preferablyincludes an interior sealing flap 38a for sealing the upper portion ofthe housing adjacent the joint between the opposing edges of thehousing. A tape wrapping, not shown, may also be used to secure the heatshield 37 in position until the heat recoverable housing is properlypositioned around the main cable 21.

A first bonding clamp 41 and a second bonding clamp 42 are secured torespective first and second metallic shield end portions, and a wire 43is connected between the clamps to maintain the electrical continuity ofthe metallic cable shield 32. As shown in greater detail in FIGS. 3through 5, the first clamp 41 includes a shoe 41a and an upstandingthreaded stud 41b connected thereto. The shoe 41a is positioned underthe metallic cable shield 32 and a top plate 41c is positioned overlyingthe metallic shield. A suitable crimp connector 43a secured to the endof the wire 43 may also be positioned onto the threaded stud 41b andsecured by a suitable locking nut 41d as illustrated.

Referring now briefly to FIG. 17, a cable 21' having a single centralbuffer tube 26' is illustrated having a pair of lengthwise extendingmetallic strength members 27'. These strength members 27' are desirablycaptured or positioned so that the ends do not move and puncture ordamage any adjacent components. In the illustrated embodiment, the endsof the strength members 27' are tucked back into the cable underlyingthe shield 32' or adjacent coveting 30'. The strength members 27' may befurther secured by a tape wrapping, not shown. Alternatively, thestrength members 27' may be secured to a bonding clamp of the typedescribed in copending application entitled FIBER OPTIC BONDING ASSEMBLYAND ASSOCIATED METHOD, assigned to the assignee of the presentinvention.

For certain cable types (for example, Siecor EST), the distribution anddrop cable strength members are secured by the sleeve, sleeve adhesive,and Tye-Wraps in order to allow field deployment via the recommendedprocedure of strength member axial pull. The strength members, which arefolded back, are protected from shield laceration by a Tye-Wrap. Thestrength members are folded back across the shield approximately 1 inch.The strength members are initially secured with a Tye-Wrap.Subsequently, the XAGA sleeve is shrunk and adds additional axial pullstrength.

Referring briefly again to FIG. 2, the second bonding clamp 42additionally includes a strap member 44 cooperating therewith to securethe end of the fiber optic drop cable 22 to the main cable 21. Thus, thestrap member 44 electrically connects the drop cable metallic shield 23to the metallic shield 32 of the main cable 21 and, moreover, permitsadjustment of the position of the end of the drop cable to ensure properpositioning of spliced together fiber portions as described in greaterdetail below.

Referring now to FIGS. 2, 3 and 6, and 12-14 another aspect of thepresent invention is illustrated. Water may enter an unintendedpenetration in the cable sheath 32 remote from the splice closure 24 andmigrate through the cable and into the splice closure. Accordingly, thecable sheath end portions of the main cable 21 are desirably sealed bysealing means to prevent water entry into the splice closure 24 at therespective first and second cable sheath end portions. The sealing meansis preferably provided by respective blocking dams 45, 46 formed of awrapped compressible foam strip, and respective C-shaped bodies 47, 48of heat flowable material, which when heated flow to fill the voidsunderlying the heat recoverable housing 38 adjacent the respectiveblocking dams 45, 46.

As would be readily understood by those skilled in the art, the heatflowable material is preferably a conventional type of heat flowablematerial, for example, as supplied in small pellet form contained withina mesh pouch in copper cable technology for sealing splices. Moreparticularly, the heat flowable material preferably has a relativelyabrupt melt flow point at about 90°-95° C. The C-shaped bodies 47, 48 ofthe heat flowable material are also positioned to surround theunderlying components and thus be adjacent the housing 38 to facilitatethe transfer of heat through the housing and to the C-shaped bodies.

For a main cable 21 of the stranded buffer tube design as illustrated,the sealing means also preferably includes concentric C-shaped spacers48 positioned onto respective buffer tubes 26 (FIG. 3) in an alternatingor staggered arrangement as illustrated. The spacers 48 serve to spreadthe buffer tubes 26 out into spaced apart relation at the cable sheathend portions, to thereby facilitate the flow of the heat flowablematerial to fully seal the cable sheath end portions.

As illustrated best in FIGS. 12 through 14, as heat is applied to causethe heat recoverable tube or housing 38 to shrink down onto theunderlying components, the C-shaped body of heat flowable material isalso melted and flows to fill the voids adjacent the buffer tubes 26. Inone embodiment, the heat recoverable housing 38 may be transparent topermit viewing of the interior of the housing to assure proper flow ofmaterial. In addition, a visible bump or protrusion would also indicatethat secondary heating may be required to melt the C-shaped bodies.

The concentric spacers 48 further serve to separate the buffer tubes 26so that the cable sheath end may be completely sealed. As would bereadily understood by those skilled in the art, the C-shaped body ofheat flowable material 47, blocking dam 45 (FIG. 6) and heat recoverablehousing 38 may be used to seal cable sheath end portions of cables forother applications, such as involving conventional in-line or buttsplice closures for aerial or buried installation. In addition, thisaspect of the invention may be applied to a single central buffer tubecable, and a single spacer may optionally be used to ensure flow to sealthe area between the cable shield and the underlying central buffertube. To facilitate sealing of stranded buffer tube cables, theconcentric spacers 48 are also desirably used.

Referring now to FIGS. 7 through 10, the fiber guide means 34 and itsinstallation and functions are explained. As shown in FIG. 8, respectiveend portions of a pair of predetermined optical fibers 50 are extendedoutwardly from a first opening 51 in a respective buffer tube 26, byfirst making a second opening 52 in the same buffer tube 26 at alocation downstream from the first location and adjacent a secondlocation whereat the drop cable 22 is secured to the main cable 21. Theopenings 51, 52 in the buffer tube 26 may be readily made using aconventional procedure as outlined, for example, in Siecor OperatorManual SOM-004-026 Issue 2 (September 1988) entitled SIECOR™ No-SlackOptical Fiber Access Tool.

The predetermined optical fibers are severed at the second opening 52and pulled back to extend outwardly from the first opening 51. Thespacing between the first and second openings 51, 52 is preferably abouta foot to thereby provide sufficient slack for several splice attemptsusing a conventional fusion splicer, as would be readily understood bythose skilled in the art. This relatively short length of fiber may bereadily withdrawn from the buffer tube 26 without a substantiallikelihood of damaging the fibers.

As would also be readily understood by those skilled in the art, a maincable 21 of the type having a single central buffer tube may also beaccessed by cutting a longitudinally extending slit in the buffer tubefrom a first location to a second location. The optical fibers may besevered at the first location, thereby creating a predetermined lengthof slack optical fiber for subsequent splicing.

The fiber guide means 34 preferably includes an elongate robe 55 havinga longitudinally extending slot 56 therein for receiving therein splicedtogether fiber portions 50, 57 of the main cable 21 and drop cable 22,respectively. The spliced together fiber portions 50, 57 are positionedwithin the fiber guide means 34 extending in a substantiallylongitudinal direction adjacent the main cable 21. Moreover, the lengthof the elongate tube 55 substantially corresponds to the length of thespliced together fiber portions.

In other words, the spliced together fiber portions 50, 57 arepositioned within the elongate tube 55 devoid of a slack coil of opticalfiber. Accordingly, the outer diameter of the splice closure 24 may begreatly reduced over prior art designs which required that the closurebe sufficiently large to accommodate the minimum bend radius of anoptical fiber.

As shown in FIGS. 2 and 11, another feature of the invention is that thedrop cable 22 preferably includes a central buffer tube 28 having an endportion positioned within an adjacent end portion of the elongate tube55 of the fiber guide means 34. The fiber guide means 34 also preferablyincludes a pair of longitudinally extending arcuately shaped walls 58,59 connected to the elongate tube 55 and gripping adjacent portions ofthe buffer tubes 26 of the main cable 21. The elongate tube 55 andarcuately shaped walls 58, 59 may be integrally molded plastic, forexample, to reduce the number of component parts.

A foam cushion layer 61 (FIGS. 7 and 9) is preferably provided betweenthe buffer tubes 26 of the main cable 21 and the arcuately shaped walls58, 59 of the fiber guide means 34. A plurality of longitudinally spacedapart fasteners, such as tie wraps 63, preferably surround the maincable 21, pass through suitable openings in the fiber guide means 34,and surround the pair of arcuately shaped walls 58, 59 to thereby securethe fiber guide means 34 to the main cable. The foam cushion layer 61resists twist of the guide means 34 independently of the tubes, whichmight otherwise result in pinched fibers.

As shown best in the exploded view of FIG. 9, the elongate tube 55includes a slotted opening 64 extending inwardly from a first endthereof. This slotted opening 64 permits the fiber guide means 34 to bepositioned over the underlying first opening 51 of the buffer tube 26 toprotect the opening and permit routing of fiber end portions 50 into theelongate tube. The fiber guide means 34 also preferably extendslongitudinally to cover the second opening 52 in the buffer tube 26 andthereby protect this opening as well. As shown in FIGS. 2 and 7, thewire 43 for maintaining electrical continuity of the metallic shield 32is preferably positioned in side-by-side relation with the elongate tube55 of the fiber guide means 34 to thereby further reduce the requiredexterior diameter of the splice closure 24.

The end portions of the drop cable optical fibers 57 may be splicedtogether with respective end portions of the predetermined opticalfibers 50 of the main cable 21 by conventional means, such as fusionsplicing or mechanical splicing as would be readily understood by thoseskilled in the art. For example, for conventional fusion splicing,protective sleeves 50a, 50b may be secured surrounding the fusionsplices (FIG. 10). In addition, the respective lengths of the fibers 50,57 may be selected to provided the longitudinally staggered relationshipof the protective sleeves 50a, 50b as in the illustrated embodiment.

Referring now to FIG. 16, another embodiment of fiber guide means 34'according to the invention is illustrated. The fiber guide means 34'includes an elongate tube 55' having an elongate opening 56' and asomewhat square cross-sectional shape, although other configurations arecontemplated by the present invention. The embodiment includes a cover68 integrally molded with the elongate tube 55' and the dependingsidewalls 58', 59'. The interior of the sidewalls 58', 59' also includelongitudinal ribs 69 for gripping adjacent portions of the main cable21. The interior of the elongate tube 55' may be filled with a gel, notshown, to prevent movement of the spliced together fiber portions 50therein.

Referring now to FIGS. 18-20 a first embodiment of a strain relief orguide means 40 in combination with a heat recoverable housing 38 andcable 21 according to another aspect of the present invention areillustrated being assembled. The strain relief or guide means 40 ispreferably positioned on each end of the splice closure housing 38(FIG. 1) to provide both strain relief and to assist in guiding theclosure through a conduit, for example. While the strain relief or guidemeans 40 may preferably be used in combination with the splice closure24 for the main cable 21 and drop cable 22 as shown in FIG. 1, those ofskill in the art will readily understand that the strain relief or guidemeans may be used in other splicing arrangements as well, such as inconventional copper cable splices.

More particularly, the cable 21 has a first degree of flexibility, whilethe heat recoverable housing 38 surrounding the cable splice will have asecond degree of flexibility higher than the first degree of flexibilityof the cable. The housing 38 also includes an end opening through whicha portion of the cable emerges. As shown in the illustrated embodiment,a portion of heat flowable material 104 is shown adjacent the endopening of the housing 38.

The strain relief or guide means 40 is secured to the emerging portionof the cable 21 immediately downstream from the end opening of thehousing 38 to provide strain relief to the emerging cable portion. Thestrain relief or guide means 40 includes an elongate body 100 and meansfor securing the elongate body to the emerging cable portion. Theelongate body 100 preferably has a predetermined degree of flexibility,for producing in combination with the emerging cable portion, a thirddegree of flexibility between the first and second degrees offlexibility to thereby provide strain relief to the emerging cableportion.

The housing 38 is preferably provided by a sheet of heat recoverablematerial having a pair of abutting longitudinally extending edgeportions 38b (FIG. 1), and a clamp member 39 for securing the edgeportions together thereby defining an enlarged circumferential portionfor the housing. Accordingly, the elongate body 100 preferably furtherincludes a longitudinally extending tapered portion 103 aligned with theenlarged circumferential portion for facilitating passage of said spliceclosure through a conduit.

In the illustrated embodiment of the invention, the clamp member 39 hasan end portion extending longitudinally outwardly a predetermineddistance beyond adjacent edge portions 38b of the sheet of heatrecoverable material. Accordingly, a portion of the elongate body 100adjacent the tapered portion 103 has a recess 105 therein receivingtherein the end portion of the clamp member 39. A tape wrapping 105 ispreferably used to secure the elongate body 100 to the cable 21 and theclamp member 39. The extending end of the clamp member 39 serves tomaintain the elongate body 100 in proper rotational alignment with theenlarged circumferential portion of the housing 38.

A second embodiment of the strain relief or guide means 40' is shown inFIGS. 21 and 22. Like elements are indicated by prime notation and thusneed not be described further. In the illustrated embodiment, theelongate body 100' surrounds the cable 21 and thus is preferably formedof mating halves to facilitate installation. In addition, the elongatebody 100' preferably includes a second or tapered distal end portion 108immediately adjacent the cable 21 for further facilitating passage ofthe splice closure through a conduit. The elongate body 108 alsopreferably includes a proximal end portion 109 (FIG. 22) extendinglongitudinally into the end opening of the heat recoverable housing 38and between the cable 21 and the housing, thus, providing even greaterstrain relief capability. A fastener, such as a tie wrap 110 may be usedto secure halves of the elongate body 100' to the cable 21.

Referring now to additionally to the flowchart of FIG. 15, method stepsaccording to the present invention are described. If a preterminatedfiber optic system is being made, the following steps explained woulddesirably be performed in a factory environment; however, the steps mayalso be performed in the field, for example, to add a drop cable 22 toan existing main cable 21. Upon starting (Block 70), a technician cutsback the cable sheath 31 of the main cable 21 at Block 72. Other cablecomponents may also be removed, such as an aramid yarn layer 29 andsurrounding covering 30. The predetermined fiber end portions 50 fromthe main cable 21 are then separated from other fibers and extendedoutwardly from the respective buffer tube 26 (Block 74).

The fiber guide means 34 extensively described above is then positionedon the exposed portion of the buffer tubes of the main cable 21 (Block76). At Block 79, if the cable has a metallic shield 32, at Block 78 thebonding clamps 41, 42 and the interconnecting wire 43 are installed ontothe respective metallic shield end portions to maintain the electricalcontinuity of the shield 32.

The respective end portions of the optical fibers of the main and dropcables are spliced together at Block 80 and positioned through thelongitudinal opening 56 of the elongate tube 55 so that the splicedtogether fiber portions 50, 57 are secured within the elongate tube 55and are devoid of slack coils of optical fiber to thereby provide acompact splice closure 24 (Block 82).

The end of the drop cable 22, and more particularly, the exposed portionof the metallic shield 23 may be positioned within the strap 44 of thesecond bonding clamp 42 and its position adjusted to maintain a desirednontaut condition in the spliced together fiber portions 50, 57 (Block84). A cover 68 (FIG. 16) may be positioned over the elongate tube 55'to cover its longitudinal opening 56'.

At Block 86, the blocking dams 45, 46 are positioned adjacent the endsof the fiber guide means 34, and the respective C-shaped heat flowablematerial bodies or rings 47, 48 are positioned surrounding the buffertubes 26 (Block 88). The concentric spacers 48 may also be positionedaround the buffer tubes 26 to spread the buffer tubes into spaced apartrelation.

At Block 90, the heat shield 37 and heat recoverable housing 38 arepositioned surrounding the main cable 21 and underlying fiber guidemeans 34. Accordingly, at Block 90 the housing 38 is heated to its heatrecovery temperature, such as using a conventional oven or torch as usedfor similar heat recoverable housings for copper cables. During heatingof the housing 38, the C-shaped bodies 45, 46 of heat flowable materialmay melt and flow to completely seal the cable sheath end portions. AtBlock 91 if heat flowable material bodies have not been sufficientlyheated to melt and flow, bumps in the housing may be visible, and if so,a secondary heating step (Block 92) will melt the bodies and cause thematerial to flow and fill the voids at the cable sheath end.

For a single field-installed drop cable and its associated spliceclosure, the splice closure and drop cable may then be installed intotheir desired positions. For a preterminated fiber optic system, atBlock 92 the splice closure 24 and the respective portions of the maincable 21 and the drop cable 22 may be wound onto a takeup reel 25 andthe process repeated for a desired number and position of a series ofdrop cables (Block 94). The preterminated cable may then be shipped andplaced along its desired route in the field.

Many modifications and other embodiments of the invention will come tothe mind of one skilled in the art having the benefit of the teachingspresented in the foregoing descriptions and the associated drawings.Therefore, it is to be understood that the invention is not to belimited to the specific embodiments disclosed, and that modificationsand embodiments are intended to be included within the scope of theappended claims.

That which is claimed is:
 1. A fiber optic cable splice closure of thetype for joining a fiber optic main cable to a fiber optic drop cable,the fiber optic main cable comprising a buffer tube having an opening ata first location, and at least one optical fiber having an end portionextending through the opening at the first location, the fiber opticdrop cable having an end secured to the main cable at a second locationdownstream from the first location, the fiber optic drop cablecomprising at least one optical fiber having an end portion extendingoutwardly from the end of said drop cable, the end portion of the atleast one optical fiber of the drop cable being spliced together with anend portion of the at least one optical fiber of said main cable therebydefining at least one spliced together fiber portion, said spliceclosure comprising:fiber guide means adapted for extending adjacent themain cable between the first and second locations and for guiding the atleast one spliced together fiber portion adjacent the main cable in agenerally longitudinal direction devoid of a slack coil of opticalfiber, said fiber guide means comprising: an elongate tube having alogitudinally extending slot therein adapted for receiving therein thespliced together fiber potions, and tube securing means adapted forsecuring said elongate tube to the main cable; anda housing surroundingthe main cable and said fiber guide means.
 2. A fiber optic spliceclosure according to claim 1 wherein said tube securing means comprisesa pair of longitudinally extending arcuately shaped walls connected tosaid elongate tube and adapted for gripping adjacent portions of saidmain cable.
 3. A fiber optic splice closure according to claim 2 whereinsaid fiber guide means further comprises a foam cushion layer adaptedfor underlying said arcuately shaped walls of said tube securing means.4. A fiber optic splice closure according to claim 1 wherein the fiberoptic main cable is of the type further comprising a metallic shieldsurrounding the one or more buffer tubes; wherein a longitudinallyextending portion of the metallic shield is removed from the main cableand defines first and second metallic shield end portions adjacentrespective first and second locations along the main cable; and furthercomprising electrical connection means adapted for electricallyconnecting the first and second metallic shield end portions together tomaintain continuity of the metallic shield.
 5. A fiber optic spliceclosure according to claim 4 wherein said electrical connection meanscomprises a predetermined length of wire, and first and second bondingclamps adapted for securing opposing ends of the wire to respectivefirst and second metallic shield end portions.
 6. A fiber optic spliceclosure according to claim 5 wherein said second bonding clamp includesstrap means adapted for securing the fiber optic drop cable to the maincable at the second location.
 7. A fiber optic cable system according toclaim 6 wherein the drop cable is of the type including a metallicshield, and wherein said strap means is adapted to surround an endportion of the shield of the drop cable for electrically connectingthereto.
 8. A fiber optic cable splice closure of the type for joining afiber optic main cable to a fiber optic drop cable, the fiber optic maincable comprising an outer sheath surrounding the one or more buffertubes, wherein a longitudinally extending portion of the sheath isremoved from the main cable and defines first and second cable sheathend portions adjacent respective first and second locations along themain cable, at least one such buffer tube having an opening at a firstlocation, and at least one optical fiber having an end portion extendingthrough the opening at the first location, the fiber optic drop cablehaving an end secured to the main cable at a second location downstreamfrom the first location, the fiber optic drop cable comprising at leastone optical fiber having an end portion extending outwardly from the endof said drop cable, the end portion of the at least one optical fiber ofthe drop cable being spliced together with an end portion of the atleast one optical fiber of said main cable thereby defining at least onespliced together fiber portion, said splice closure comprising:fiberguide means adapted for extending adjacent the main cable between thefirst and second locations and for guiding the at least one splicedtogether fiber portion adjacent the main cable in a generallylongitudinal direction devoid of a slack coil of optical fiber; and ahousing surrounding the main cable and said fiber guide means, saidhousing including a heat recoverable material and a heat shield layerunderlying said heat recoverable material for protecting said fiberguide means when heating said housing.
 9. A fiber optic splice closureaccording to claim 8 wherein said splice closure further comprisessealing means contained within said heat recoverable housing adjacentopposing first and second ends thereof and adapted for sealing adjacentcable sheath end portions of the main cable, and wherein said sealingmeans comprises first and second masses of heat flowable materialadjacent respective first and second cable sheath end portions.
 10. Afiber optic splice closure according to claim 9 wherein each of saidsealing means further comprises first and second blocking dams adjacentrespective first and second ends of said fiber guide means forpreventing flow of said heat flowable material into said guide means,and wherein each of said blocking dams comprises a compressiblematerial.
 11. A fiber optic splice closure according to claim 9 whereinsaid main cable is of the type including a plurality of buffer tubes,and wherein said sealing means further comprises first and secondpluralities of concentric spacers adapted for surrounding predeterminedones of said plurality of buffer tubes adjacent respective first andsecond cable sheath end portions for maintaining said buffer tubes inspaced apart relation to facilitate flow of said heat flowable materialinto voids between said spaced apart buffer tubes.